ABLE-MCP Ableton Extension (.ablx)

This is the official Ableton Extension API 1.0 bridge for ABLE-MCP. It runs inside Live's Extension Host (Node 22) and exposes a WebSocket JSON-RPC 2.0 server that the Python MCP server connects to.

It is the recommended bridge for Live 12 with the Extensions feature enabled. The legacy Max for Live bridge remains available for older setups and for transport-control workflows.

Wire protocol

• Endpoint: ws://127.0.0.1:9831 (override with ABLE_MCP_BRIDGE_HOST / ABLE_MCP_BRIDGE_PORT env vars in Live).
• On connect the server sends a notification: {"jsonrpc":"2.0","method":"bridge.hello","params":{"protocol":"able-mcp/0.2-ext","version":"0.1.0"}}
• Identical method names to the M4L bridge so the Python BridgeClient is unchanged.

Methods

Stable across both bridges:

• ping
• song.getTempo, song.setTempo
• song.getState (transport fields are null in the extension; see below)
• song.listTracks
• track.create (the M4L index arg is rejected — extension always appends)
• track.delete, track.rename
• clip.createMidi (session slot only; index arg rejected)
• clip.setNotes (replaces all notes — server normalizes input)
• clip.delete

Extension-only (not in the M4L bridge):

• audio.import — import a WAV/AIFF into the project, place in session slot or arrangement
• audio.renderTrack — render pre-FX audio of an arrangement track to WAV
• arrangement.createMidiClip — create empty MIDI clip in arrangement
• scene.create
• env.info — storage/temp dirs, Live UI language

Not supported by the SDK 1.0 beta (the methods exist but return JSON-RPC error -32000):

• Transport: transport.isPlaying, transport.play, transport.stop, transport.continue
• View selection: view.getSelection
• song.undo, song.redo (the SDK auto-undoes mutations and groups them via withinTransaction)

Use the M4L bridge for those workflows until the API exposes them.

Build

Requires Node 22+ and npm. The Ableton SDK and CLI tarballs in ../extensions-sdk-1.0.0-beta.0/ are loaded via file: deps; no SDK access to npm registry is needed.

cd extension
npm install
npm run build         # dev bundle with sourcemaps -> dist/extension.cjs
npm run build:prod    # minified bundle
npm run package       # production build + ../dist/AbleMCP.ablx

npm audit should report 0 vulnerabilities. We pin ws ≥ 8.21.0 and tsx ≥ 4.22.4 to clear known CVEs.

Smoke test (no Live required)

tests/smoke.js boots the same RpcServer on port 9842 with stub methods and round-trips: bridge.hello, ping, error mapping, method-not-found, and a fake song.getTempo.

npm run smoke

Install in Live

1. Copy dist/AbleMCP.ablx to Live's Extensions directory (see Live's "Extensions" preference page for the platform-specific path).
2. Restart Live. The extension activates automatically.
3. Live's Extension log should show bridge listening on ws://127.0.0.1:9831.
4. From the Python side, run the live_check_bridge MCP tool — you should see protocol: "able-mcp/0.2-ext".

Environment variables (read at activation)

• ABLE_MCP_BRIDGE_HOST (default 127.0.0.1)
• ABLE_MCP_BRIDGE_PORT (default 9831)

Bind to localhost only. The bridge has no authentication; do not expose it on a network interface.

Layout

extension/
  manifest.json        # Ableton extension manifest
  package.json
  tsconfig.json
  build.ts             # esbuild bundler (CJS, node22, all deps inlined)
  src/
    extension.ts       # activate() entry point
    rpc.ts             # WebSocket JSON-RPC 2.0 server
    methods.ts         # SDK-typed method implementations
  tests/
    smoke.js           # offline wire-protocol smoke test